The invention relates to a valve mechanism for an internal-combusion engine.
In a known valve mechanism of the relevant generic type (e.g. EP 275,715), the lubrication of the sliding surfaces of the rockers takes place via bores connected to lubricating-oil lines which are arranged above the camshaft and parallel to the latter. At the same time, each rocker sliding surface or each cam has its own bore. This method of lubrication involves an extremely high outlay.
The object of the invention is to provide a valve mechanism of the relevant generic type, in which the lubrication of the rocker sliding surfaces takes place at a substantially lower outlay.
In the known valve mechanism, the rockers and their sliding surfaces are arranged at a distance from one another. Whereas, in the proposal according to the invention the rockers bear against one another, specifically in such a way that their sliding surfaces are aligned at least intermittently with one another and form an essentially continuous surface. This occurs whenever at least the base circles of the cams are identical. The lubrication of this surface consisting of a plurality of sliding surfaces can take place via one or more lubricating-oil bores, but in this case the number of lubricating-oil bores is smaller than the number of sliding surfaces. It has been shown that, at least in an arrangement of three rockers cooperating with their own cams, a lubricating-oil feed to the sliding surface of the middle rocker is sufficient also to lubricate the sliding surfaces of the two outer rockers, since the lubricating oil is then distributed over the sliding surfaces of all the rockers when these sliding surfaces are aligned with one another. In a valve mechanism having four rockers per cylinder, which are actuated by the cams of a common camshaft, it is expedient to provide lubricating-oil bores for the two middle rockers, in order to achieve a uniform lubrication of all the sliding surfaces. In a valve mechanism having five rockers cooperating with their own cams, a lubricating-oil bore for the middle rocker can be sufficient for lubricating all the rocker sliding surfaces, but it can prove expedient, in this case, to provide a lubricating-oil bore for the second and the fourth rocker each. In all instances, however, the number of lubricating-oil bores is smaller than the number of rocker sliding surfaces, so that these bores can have a larger diameter than in an arrangement in which a lubricating-oil bore is provided for each rocker and should have only a small diameter in order to keep the throughflow low. Larger bores can be produced more easily and are less inclined to become clogged. In the proposal according to the invention, therefore, a reliable lubrication of a plurality of rocker sliding surfaces is achieved by means of a smaller number of larger lubricating-oil bores.
The lubricating-oil feed can take place according to EP 275,715 or, as is known, for example, from German Offenlegungsschrift 2,703,519, by feeding the lubricating oil to the cam sliding surfaces through a longitudinal channel in the camshaft.
In order to ensure that the rockers of each rocker group assigned to a cylinder bear against one another, it is preferable to arrange an outer rocker so as to be axially non-displaceable, for example in bearing contact at a bearing point of the rocker shaft, and to mount the remaining rockers on the common shaft so as to be axially displaceable and provide means which exert on all the other outer rockers an axial force acting in the direction of the first outer rocker, in order to press all the remaining rockers against one another and against the first outer rocker. This axial force can be generated by a spring which is provided between the second outer rocker and a fixed support. This support can itself be formed by a retention or a mounting of the common pivot shaft.
Although, in the proposal according to the invention, the lubricating-oil bores in the cam or cams can have a larger diameter than in an arrangement of a lubricating-oil bore in each cam, the production of relatively long bores of this type presents problems. In order to remedy this, according to another feature of the invention, a nozzle having a smaller passage cross-section is inserted into the lubricating-oil bore. The lubricating-oil bore itself can thus have a larger diameter and be produced without difficulty. The nozzle preferably consists of a material which is softer than the material of the cam, so that, when pressed into the bore, it can experience deformation and the accuracy of the bore can be kept low. Alternatively, the lubricating-oil bore can have a first portion of small diameter adjacent to the longitudinal channel and a second portion of larger or increasing diameter adjacent to the first portion and reaching as far as the cam contact surface. By this means too, the production of the lubricating-oil bore becomes simpler and easier, since only a short portion of the lubricating-oil bore has a small diameter. This short portion can be produced by drilling or also by laser beam.
The supply of the longitudinal channel with lubricating oil preferably takes place via a camshaft bearing. A camshaft bearing of this type conventionally has a screwed-on bearing cover with passage holes for screws. So that a passage hole of this type can be provided at as short a distance as possible from the camshaft on one side of the camshaft, the supply of lubricating oil to the longitudinal channel takes place via an eccentric circumferential groove in the bearing surface of the camshaft bearing, the radial width of this circumferential groove being very small or even zero on one side of the camshaft, so that, on this side, the passage bore can be brought very close to the camshaft. The feed of lubricant takes place in the wider region of the circumferential groove. The transfer of lubricating oil out of the circumferential groove into the longitudinal channel in the camshaft takes place by means of a transverse bore passing through diametrically in the camshaft.